This invention relates to an improved method of locating and supporting a ceramic core in fixed space relationship in a ceramic shell mold and maintaining this fixed space relationship in the subsequent casting process for production of a hollow metal casting.
In the investment casting i.e. the "lost-wax" process for the production of hollow metal castings, it is known to encase a core in wax through which platinum pins are inserted until the pins are in contact with the core, prior to coating the wax encased core with a shell of ceramic slurry, so that on hardening the shell and thereafter removing the wax, the core remains supported in a fixed space relationship with the shell.
Disadvantages of this known method of core support that the pins,
(a) are manufactured from platinum which whilst being inert with many materials, is expensive,
(b) the platinum pins melt on casting the metal and dissipate into the casting during solidification. The now unsupported core may move from its precise location,
(c) the platinum pins whilst sometimes supporting core lengths up to 12.5 cms, are unable to adequately support longer core lengths, resulting in the need for use of the known process of "core printing", whereby the core is extended to provide flattened ends which may then be gripped in the wax pattern die prior to encasing the core with wax. The core length is extended sufficiently so that after encasing the core with wax and then removing the wax pattern die prior to coating the wax encased core with a ceramic slurry material to form the shell, the core prints protrude through the ceramic shell. The core printing method has the disadvantage that on subsequent removal of the core from the casting, manufacturing steps have to be added to blank off an aperture which the core printing causes to be produced at the blade tip.